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Title: Assessing the suitability of American National Aeronautics and Space Administration (NASA) agro-climatology archive to predict daily meteorological variables and reference evapotranspiration in Sicily, Italy

Author
item NEGM, AMRO - University Of Palermo Italy
item Jabro, Jalal - Jay
item PROVENZANO, GIUSEPPE - University Of Palermo Italy

Submitted to: Agricultural and Forest Meteorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/29/2017
Publication Date: 10/15/2017
Publication URL: http://handle.nal.usda.gov/10113/5700736
Citation: Negm, A., Jabro, J.D., Provenzano, G. 2017. Assessing the suitability of American National Aeronautics and Space Administration (NASA) agro-climatology archive to predict daily meteorological variables and reference evapotranspiration in Sicily, Italy. Agricultural and Forest Meteorology. 244-245:111-121. doi:10.1016/j.agrformet.2017.05.022.

Interpretive Summary: The suitability of the POWER-NASA database to estimate daily reference evapotranspiration, ET0, was assessed in Sicily for the period 2006–2014. Daily ET0 values, estimated according to the FAO-56 PM equation by using the POWER-NASA agro-climatology open access archive, were compared to the corresponding evaluations according to the data measured on 30 meteorological ground stations installed in Sicily, Italy. The analyses considering the climate variables evidenced a fairly good agreement between ground measurements and the corresponding data available at the POWER-NASA archive. The estimates of ET0 resulted from the data available on the POWER-NASA agro-climatology archive were comparable to those estimates obtained by using climate data recoded by 30 ground SIAS stations, with RMSE values ranging between 0.68 mm d-1 and 1.27 mm d-1 and MBE varying between -0.39 mm d-1 and 0.73 mm d-1. The greatest differences of ET0 in term of RMSE values are greater than 1 mm d-1, as the case of stations ID 250, 302, 308, 231, 246, 258 and 286, resulted as a consequence of many factors. First, great differences were observed between the two databases in term of air relative humidity, which, in comparison with other variables, represents the highest RMSE and MBE values and corresponds on average to 12.2% and 1.3% respectively. It is recommended to enhance the estimates of air relative humidity acquired by means of the POWER-NASA archive as the error of those estimates greatly influences the error associated to ET0_NASA estimates. Second, there are small differences between the two databases in term of solar radiation which corresponds on average to RMSE and MBE values of 2.7 MJ/m-2 d-1 and 0.7 MJ/m-2 d-1, respectively. Third, the location and altitude of the area plays an important role; it was noticed that some of the stations (ID 250, 231, 246, and 258), located in the northern part of Sicily are characterized on average by relatively high altitude˜ 600 m a.s.l., facing the effect of versant coming out of surrounded mountains. Nonetheless, all of these factors affect the ET0-NASA estimates, although our results clearly show that the correlation between the POWER-NASA observations and the records of the ground station as well as ET0-NASA and ET0-SIAS estimates are fair. In general the POWER-NASA archive is adequate to evaluate ET0 over the areas where most of the climate variables are not measured in term of the factors influencing the estimation processes.

Technical Abstract: For decades, the importance of evapotranspiration processes has been recognized in many disciplines, including hydrologic and drainage studies, irrigation systems design and management. A wide number of equations have been proposed to estimate crop reference evapotranspiration, ET0, based on the variables affecting the process. When a full data set of weather variables is available, the Food and Agriculture Organization (FAO) of the United Nations has recommended the use of the physically- based FAO-56 Penman-Monteith equation. In this research, the suitability of the Prediction Of Worldwide Energy Resource (POWER)-NASA database to estimate daily meteorological variables and reference evapotranspiration was assessed in Sicily, Italy for the period 2006-2014, based on ground data measured by a network of climate stations belonging to the regional Agro-meteorological Information Service (SIAS). After comparing the climate data (minimum, maximum and average air temperature and relative air humidity, solar radiation and wind speed) available in both databases, a statistical comparison was carried out on ET0 values estimated according to the FAO-56 PM equation. The analysis showed a good correlation between the climate variables of both the databases; in addition, ET0 values estimated with POWER-NASA database were comparable to those obtained by using the SIAS records with RMSE values ranging between 0.68 mm d-1 and 1.27 mm d-1 and MBE varying between -0.39 mm d-1 and 0.73 mm d-1. The results support the possibility of obtaining suitable estimates of daily ET0 based on the POWER-NASA agroclimatology archive, even to other Mediterranean countries where most of the climate variables are not measured.